The use of fans for blowing air over an electronic circuit board for cooling purposes is well known in the art. Typically, this is accomplished using either piezoelectric or rotary type fans.
Rotary type fans have many drawbacks. They require many moving parts including bearings, which necessarily require some type of lubrication. Rotary fans also have typically larger size and power consumption requirements than piezoelectric fans and rotary fans may generate significant electromagnetic interference (EMI) and radio frequency interference (RFI) noise signals. Additionally, rotary fans oftentimes have a shorter life than piezoelectric fans.
Piezoelectric fans have been used as an alternative to rotary fans and offer significant advantages in that they have fewer moving parts, generate very little heat, and can be used in harsh environments with wide temperature ranges, wide humidity ranges, or even in hazardous and explosive gas conditions.
Prior art piezoelectric fans have typically been manufactured using a dual-blade design. The two bender blades are typically oscillated 180 degrees out of phase with each other. The complementary back and forth motion of the two blades provides dynamic balancing and also minimizes vibration and noise in the device. Unfortunately, dual-blade piezoelectric fans have a profile (height above a circuit board) which is unacceptably high for many applications.
FIG. 1 shows a dual-blade piezoelectric fan 100 in accordance with the prior art. In FIG. 1, a housing 102 supports two fan blades 104 and 104' which are driven 180 degrees out of phase with each other. Piezoelectric elements, internal to the housing 102, are activated by a pair of lead wires 106, 106'. The air flow patterns around the blade 104' are represented by arrows which show the air flow in and out of fan 100. Prior art fans, such as the one shown in FIG. 1, have a very high profile and also consume a large volume of space. Although they may be readily used in applications where space restrictions are not an issue, they are ill-suited for cooling densely packed electronic components in modern electronic products.
FIG. 2 shows another embodiment of a flat dual blade piezoelectric fan 200 found in the prior art. Fan 200 contains two fan blades 202, 202' which are separated by a mounting beam 203. Each of the fan blades contains a piezoelectric element 204 which is driven to cause deflection in the fan blades 202, 202'. An electrical current activates the piezoelectric elements and this is shown in FIG. 2 by positive and negative lead wires attached to element 204.
The air flow patterns around the fan blades are represented by arrows which show the air flow in and out of the fan. The primary airflow in occurs at the corners of the fan 206 and the secondary airflow in occurs along the side edges of the fan 208. The air flow out of the fan occurs at an end of the fan 210 opposite the mounting beam 203.
Piezoelectric fan 200 also has significant design drawbacks. The airflow in fan 200 is non-axial and, as such, substantial volume is needed for ducting purposes. Additionally, the height of the dual-blade design may be restrictive for certain applications.
Consequently, a low-profile single-blade piezoelectric fan which offered a low-power, low-noise, low-cost, and low-vibration design and which could provide a sufficient axial flow to cool electronic components in a rugged, customized housing assembly which provided for smaller overall dimensions in electronic products would be considered an improvement in the art.